Windows setup loop — "Couldn't check Windows setup" / "Windows setup didn't finish", sandbox-setup.exe crashes silently on elevation

Environment

App: ChatGPT / Codex Desktop (Microsoft Store)
App version: 26.721.4979.0 (ChatGPT.exe 150.0.7871.128)
Package: OpenAI.Codex_26.721.4979.0_x64__2p2nqsd0c76g0
OS: Windows 11
VC++ Redistributable installed: Microsoft Visual C++ v14 Redistributable (x64) - 14.50.35719 (already up to date, confirmed via Apps & Features)

Summary
The "Finish Windows setup" screen never completes. Clicking "Try again" loops indefinitely, alternating between "Windows setup didn't finish" and "Couldn't check Windows setup." Sandboxed local execution cannot be used as a result.

Steps to reproduce

Launch ChatGPT/Codex Desktop.
App shows "Finish Windows setup."
Click "Try again" (or trigger UAC via the button).
UAC prompt appears and is accepted (Yes).
Setup fails; screen returns to "Windows setup didn't finish" / "Couldn't check Windows setup."

Additional diagnosis performed

Ran codex-windows-sandbox-setup.exe directly from C:\Users<user>\AppData\Local\OpenAI\Codex\bin<hash>\ as Administrator: process launches then disappears immediately with no visible error or window.
Checked Windows Event Viewer (Application log) for the time of the crash: no "Application Error" entry was logged for codex-windows-sandbox-setup.exe — it fails silently, no crash dump generated.
No .sandbox folder or setup_marker.json / deny_read_acl_state.json found under %LOCALAPPDATA%\OpenAI\Codex — the setup helper appears to fail before creating any sandbox state files.
Confirmed UAC itself works normally for other apps (e.g., Command Prompt "Run as administrator" triggers a normal prompt).
Reinstalled/repaired VC++ x64 redistributable — already at newer version (14.50.35719) than the official redistributable installer offered (14.44), so this wasn't the cause.
Updated the app via Microsoft Store to the latest available build — issue persisted.
Restarted the PC after update — issue persisted, same loop.
Tried "Continue with limited access" as a workaround.

Start by reproducing the elevation path with codex-windows-sandbox-setup.exe from the reported AppData\Local\OpenAI\Codex\bin<hash> directory, and inspect the Windows Event Viewer Application log. Check whether setup creates .sandbox, setup_marker.json, or deny_read_acl_state.json; done means the helper completes and the Windows setup screen no longer loops.